Various types of configurable keyboards are known in the literature. U.S. Pat. No. 4,647,911 describes a calculator with definable keys as well as a typewriter keyboard with definable keys. It is suggested in the patent that removable or erasable indicia be provided in association with the definable keys for indicating the definitions of such keys.
U.S. Pat. No. 4,431,988 describes a microprocessor-based keyboard/display unit for configuring control instruments which incorporates a configurable keyboard but does not provide means for indicating the key definitions on the keyboard.
U.S. Pat. No. 4,551,717 describes an intelligent key display wherein each key comprises a microchip device and one or more liquid crystal displays to indicate the programmed function of the key.
U.S. Pat. No. 4,385,366 describes a configurable keyboard wherein the key definition appears on a display below a transparent key and is viewed therethrough. U.S. Pat. No. 4,333,090 illustrates a similar structure.
There is described in IBM Technical Disclosure Bulletin Vol 23, No. 3, August, 1980 at page 1190 electronically changeable keyboard key inscriptions which employ liquid crystal displays in the keyboard connected by wires to a signal source.
There is described in IBM Technical Disclosure Bulletin Vol 23, No. 10, March, 1981 at page 4611 optically powered and controlled electronically alterable key labeling which employs a liquid crystal display formed in the key itself and which obtains display information optically from the base of the key.
There is described in IBM Technical Disclosure Bulletin Vol 19, No. 5, October, 1976 at page 1544 a programmed illuminated typewriter keyboard wherein display information is supplied via an optical conduit, such as an optical fiber bundle from light emitting elements to a display surface defined in the key. The optical conduit is normally fixedly attached to the key and comes into light receiving relationship with the light emitting elements when the key is in its non-depressed orientation.
There is described in IBM Technical Disclosure Bulletin Vol 22, No. 4, September, 1979, at page 1370 a programmed illuminated typewriter keyboard wherein display information is supplied via an optical conduit, such as a flexible optical fiber bundle from a light source to a display surface defined in the key.
U.S. Pat. No. 4,633,227 describes a programmable keyboard for a typewriter or similar article wherein the key definition is displayed at a window location adjacent each key. The display information is provided by mechanically movable symbol bearing strips or by LCD displays located below the key definition display locations. This structure provides a very small key definition display.
U.S. Pat. No. 4,481,508 describes a programmable keyboard wherein the functions of the keys are displayed in a dot matrix display disposed thereabove.
U.S. Pat. No. 4,441,001 describes a keyboard for inputting plural letters or symbols which is similar to that described in U.S. Pat. No. 4,633,227.